Government regulations forbid the use of milk containing more than 0.01 units of penicillin per ml in products intended for human consumption. This poses a problem for dairy producers who use large doses of Beta-lactam-type antibiotics such as penicillin to control mastitis or other diseases in dairy cows and must monitor milk for excessive quantities of these antibiotics such as penicillins or cephalosporins. An improved rapid, accurate, and easy-to-use assay procedure that can measure low concentrations of such antibiotics, particularly penicillin, in milk would be of value to the dairy industry.
A number of tests for detecting and measuring antibiotics in milk are known in the literature. U.S. Pat. No. 4,239,852 discloses a penicillin-detection test utilizing microbiological cell parts having good affinity for penicillin. The cell parts have penicillin receptor sites and the penicillin in milk competes with an added known quantity of tagged penicillin for binding to these sites. The greater the quantity of penicillin in the milk, the smaller the quantity of tagged penicillin will be accepted by the receptor sites. Thus, in a typical test, the amount of penicillin is measured as an inverse function of the amount of tagged penicillin that becomes attached to the cell parts. U.S. Pat. No. 4,239,745 discloses a somewhat similar test procedure wherein a penicillin-attracting microorganism itself, rather than a cell part thereof, is utilized.
Still another process for testing for penicillin in milk is disclosed in U.S. Pat. No. 4,347,312 wherein Brown et al disclose the use of antibody bound to a matrix as a means of anchoring penicillin selectively.
The above tests are not altogether satisfactory, because they fail to provide a simple means to measure an indicator tag directly (as opposed to inversely) proportional to the penicillin being detected, or because they are too cumbersome and expensive. These in direct competition assays are inherently less sensitive than direct tests, because the background levels with no penicillin in the milk are high and it takes a relatively greater amount of competing penicillin to reduce the level sufficiently to obtain a significant and reproducible result.
The Inventors have directed their efforts to develop a new assay which will be advantageous to the dairy operator, to the milk trucker, and to the individual farmer.